1. Field of the Invention
The invention in general relates to oxygen sensors, and more particularly to a partial pressure of oxygen sensor using the paramagnetic properties of oxygen.
2. Description of the Prior Art
In the field of gas analysis and in various oxygen utilizing systems, it is often desired to know the amount of oxygen which is present. For some systems, the amount of oxygen is an indication of system efficiency and for other systems, such as in diving systems, the amount of oxygen in the gas mixture, particularly the partial pressure of oxygen, is critical for the sustaining of life.
One type of sensor utilized extensively in the diving field is the polarographic cell, a chemical cell which is both small and relatively rugged. Such cells, however, do have a limited shelf life as well as a limited operating life.
Another type of oxygen sensor utilizes the fact that oxygen is highly paramagnetic, that is, the magnetic susceptibility of oxygen is substantially greater than that of most other gases and this characteristic is utilized to measure to a high degree of accuracy, the concentration of oxygen in a gas mixture.
A variety of types of paramagnetic gas analyzers operate on the principal of establishing a certain flux in a magnetic circuit having a plurality of air gaps. The magnetic reluctance of the gap is periodically varied by placing first a test sample and then a reference sample into the gap thereby producing a flux variation which is proportional to a particular constituent of the gas being measured, for example, oxygen.
In one type of sensor, a wheel containing alternate reference and test cells is rotated by means of a motor so that the cells pass between the gaps of the magnetic circuit while in another type of device, a toothed rotor is utilized with each tooth as it passes into a magnetic gap constituting a reference, while each space between the teeth represents a sample condition. In yet another instrument which utilizes a single air gap, a pump is utilized to alternately pump in a test gas and a reference gas into a chamber surrounding the magnetic gap.
These instruments which require multiple gaps and motor driven wheels do not lend themselves readily to a rough environmental life as would be experienced, for example, in the diving field where small size, portability, and ruggedness, as well as high accuracy, is demanded. Although a single air gap circuit would reduce the size of the overall device, the requirement for a pumping system complicates matters.
The present invention provides for a sensor which is relatively small and rugged and eliminates the requirements for rotating motors and consequently eliminates the need for bearings, rotary seals, and motor shielding devices.